(1) Field of the Invention
The present invention relates to a method and to a device for managing a loss of power on a three-engined power plant.
The invention thus lies in the field of power plants, and more particularly the field of aircraft power plants.
(2) Description of Related Art
An aircraft, and in particular a rotorcraft, may have at least one rotor contributing to providing the aircraft with propulsion and/or lift.
In order to put each rotor into rotation, the aircraft thus has a power plant. The power plant may have at least two engines driving at least one main power transmission gearbox. The main gearbox then drives the rotor in rotation via a rotor mast.
At least one engine may be a fuel-burning engine. In particular, an engine may be a turboshaft engine.
Conventionally, a turboshaft engine comprises a gas generator having at least one compressor, a combustion chamber, and a high pressure expansion assembly connected to the compressor. The compressor may be provided with a plurality of axial and/or centrifugal compression stages.
Likewise, the expansion assembly may have at least one expansion turbine. In addition, the turboshaft engine has at least one low pressure turbine that is free or that is linked to the gas generator.
The operation of a turboshaft engine is controlled by a management system. For example, a known management system is a full authority digital engine control (FADEC). A management system usually comprises a computer connected to a fuel metering unit and to various members for measuring parameters. The fuel metering unit then enables the management system to control the rate at which fuel is transmitted to the engine.
Furthermore, a fuel-burning engine and in particular a turboshaft engine may operate at a plurality of ratings.
On a multi-engined aircraft, and in particular a twin-engined aircraft, such ratings include so-called “normal” ratings that are applied in the absence of any engine failure. Such ratings are referred to as all engines operative (AEO).
Conversely, turboshaft engine ratings include so-called “contingency” ratings for use in the event of an engine failure. These emergency or “contingency” ratings are referred to as one engine inoperative (OEI) ratings.
In addition, power management systems for a twin-engined aircraft monitor the powers being developed by the engines. For example, systems for monitoring two engines communicate with each other in order to detect a loss of power from an engine. Where applicable, an indication is given to the crew signalling that an “abnormal” loss of power has occurred. For example, a display may display “power loss” when a loss of power is detected.
Such a power loss is signaled to the crew insofar a loss of power may occur before an engine failure. A pilot can then be forewarned that there is a risk of needing to use an OEI rating.
Turboshaft engines are generally balanced so that they deliver the same power. If one engine begins to lose power, the other engine compensates by delivering more power. Consequently, and particularly on a twin-engined aircraft having two turboshaft engines, a loss of power is detected by evaluating a difference between the speeds of rotation of the two gas generators of the engines, or between the torque generated by the two engines. The speed of rotation of the gas generator and the torque developed by a turboshaft engine are both images of the power being delivered by the engine.
If a management system detects a difference that is greater than a threshold, a power loss alert is then generated. This alert is a “red” alert informing the crew that one of the engines is in the process of losing power. The pilot then uses engine parameters to determine which engine is failing.
That procedure is advantageous, but it can be difficult to transpose to a three-engined aircraft, which can sometimes be overpowered. A three-engined aircraft can present special features compared with a twin-engined aircraft. For example the power developed by the engines need not be uniform.
Documents FR 3 008 957, U.S. Pat. No. 3,963,372, U.S. Pat. No. 3,969,890, EP 2 623 747, and US 2009/186320 are also known.